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ME, WILLIAM FAIKBAIKN ON 



never be less than four times the greatest load that can 

 be brought upon the bridge. In the wrought-iron Tubu- 

 lar Girder Bridge, I have computed the breaking weight 

 at twelve tons to the lineal foot, inclusive of the weight 

 of the Bridge, which is equivalent to about six times the 

 maximum load than can practically be brought upon it 



On this calculation, the following Table exhibits the 

 strengths and proportions of Girder Bridges, from 30 up to 

 300 feet span. It has been computed from experiments on 

 previously constructed Tubular Girder Bridges. 



The first column gives the length of the span clear from 

 pier to pier. 



The second, the breaking weight of the bridge in the 

 middle. 



The third, the area of the plates and angle iron of the 

 bottom of the girder. 



The fourth, the area of the cellular top. 



And the last, the depth of the girder in the middle. 

 TABLE 



SHEWINa THE PEOPORXIONS OF TUBULAR GIRDEB BRIDGES, 



FROM 30 TO 150 FEET SPAN. 



